The invention pertains to a rotatable cutting tool, which typically mounts in a stationary block (or holder) on a rotatable drum. The rotatable cutting tool engages or impinges a substrate upon the rotation of the drum. More specifically, the invention pertains to the aforementioned type of rotatable cutting tool wherein the rotatable cutting tool, which is rotatable about its central longitudinal axis, carries a superhard cutting member at the axially forward end thereof. The super hard cutting member is made from a superhard material (or includes a portion there of made from a superhard material). Superhard materials useful in the present invention include, without limitation, materials like polycrystalline diamond (PCD) or polycrystalline cubic boron nitride (PcBN).
A rotatable cutting tool typically presents a generally elongate, cylindrical geometry. The rotatable cutting tool comprises an elongate steel cutting tool body, which has an axially forward end and an opposite axially rearward end. The cutting tool body typically carries an assembly or means by which the rotatable cutting tool is rotatable carried by the stationary block or holder on the drum. Exemplary structures useful for the rotatable attachment of a rotatable cutting tool to a block or holder include those shown and described in U.S. Pat. No. 4,201,421 to Den Besten et al., U.S. Pat. No. 3,519,309 to Engle et al., U.S. Pat. No. 3,752,515 to Oaks et al., and U.S. Patent Application Publication No. US 2002/0153175 to Ojanen for a Rotatable Cutting Tool having Retainer with Dimples.
A hard cutting member typically affixes, such as by brazing, to the axial forward and of the cutting tool body. Heretofore, a hard cutting member suitable for use in a rotatable cutting tools have exhibited many different geometries. One exemplary geometry is shown and described in U.S. Pat. No. 4,497,520 to Ojanen.
Typically, the hard cutting member is made from a hard material like cemented cobalt tungsten carbide. The following patent documents disclose exemplary compositions of hard material suitable for use as a hard cutting member in a rotatable cutting tool. Further, the following patent documents disclose the use of diamond materials in the context of a rotatable cutting tool: U.S. Pat. No. 6,051,079 to Andersson et al., U.S. Patent Application Publication No. US2004/0026983 to McAlvain, and U.S. Patent Application Publication No. US2003/0209366 to McAlvain. In reference to brazing the hard cutting member to the cutting tool body, U.S. Pat. No. 4,389,074 to Greenfield, U.S. Pat. No. 5,131,725 to Rowlett et al., U.S. Pat. No. 5,429,199 to Sheirer et al., U.S. Pat. No. 6,375,272 to Ojanen, and U.S. Pat. No. 6,478,383 to Ojanen et al. discloses braze alloys that have heretofore been suitable for such a brazing operation.
In the case of a road planing machine, the rotatable drum can in many cases carry hundreds of individual blocks or holders. Each individual block or holder carries its own corresponding rotatable cutting tool, which is rotatable relative to its corresponding block or holder. It is not unusual that a rotatable drum will carry hundreds of individual rotatable cutting tools.
The road planing machine powers the rotatable drum so as to cause it to rotate. The orientation of the rotatable cutting tools with respect to the drum is such so that upon rotation of the drum, the drum drives the rotatable cutting tools into the substrate. Upon the rotatable cutting tools impinging the substrate, the substrate typically breaks thereby forming larger chunks of debris, as well as smaller particles and pieces of debris. Typically, the debris generated in a road planing operation is highly abrasive which causes the rotatable cutting tool to experience wear.
The rotatable cutting tool can experience wear in a number of ways. The hard cutting member, which is the portion of the rotatable cutting bit that first impinges the substrate, can experience wear. The initial impact of the hard cutting member against the substrate, as well as the travel of the debris along the hard cutting member, can cause this wear. Over the course of the cutting operation, the hard cutting member can lose material to the point where it becomes dull and ineffective to accomplish efficient cutting.
Another wear mechanism pertains to the braze joint between the hard cutting member and the elongate cutting tool body. Throughout the course of the cutting operation, the braze joint experiences severe stresses due to the continual intermittent violent impingement of the rotatable cutting tool against the substrate material. Over the course of time, the braze joint can experience sufficient stress so as to fail thereby allowing the hard cutting member to separate from the cutting tool body. Obviously, if the rotatable cutting tool loses the hard cutting member, the rotatable cutting tool is no longer useful for the cutting operation.
Further, during a cutting operation such as, for example, a road planing operation, debris travels down the elongate cutting tool body. Due to the abrasive nature of the debris, the elongate cutting tool body experiences wear and erosion. Since the cutting tool body typically comprises steel, those in the pertinent art characterize this wear phenomenon as “steel wash”. The result of “steel wash” is to cause the axial forward portion of the cutting tool body beneath or axially behind the hard cutting member to reduce in diameter. Such a reduction in diameter causes this portion of the cutting tool body to take on an hourglass shape. As the cutting operation continues, the axial forward portion of the cutting tool body continues to reduce in diameter to a point where it eventually breaks thereby ending the useful life of the rotatable cutting tool due to the failure of the cutting tool body.
As one can appreciate from the above description, there are a number of ways in which the rotatable cutting tool can lose its effectiveness to provide for efficient cutting. As mentioned above, it is not unusual that a rotatable drum will carry hundreds of individual rotatable cutting tools. Thus, if only a small number of rotatable cutting tools lose their cutting efficiency, the rotatable drum may continue to cut in an efficient fashion. When this is the case, the need to replace worn or failed rotatable cutting tools may not be great or at least it may not be mandatory. However, as the number of rotatable cutting tools which lose their cutting efficiency increases, the overall cutting efficiency of the rotatable drum decreases. Eventually, the cutting efficiency of the rotatable drum reaches a level that requires the operator to change the rotatable cutting tools, i.e. typically substitute new rotatable cutting tools for inoperable rotatable cutting tools.
Because of the difficulty typically inherent in removing and installing rotatable cutting tools, as well as the great number of rotatable cutting tools typically carried by a rotatable drum, the road planing machine may have to be taken out of operation for a significant amount of time. Obviously, the overall operating efficiency decreases as the amount of downtime for the road planing machine increases.
It would thus be highly desirable to provide an improved rotatable cutting tool, which is rotatably carried by an individual block or holder of a rotatable drum of a cutting machine (e.g., a road planing machine), that experiences an increase, and especially a significant increase, in useful tool life as compared to heretofore known rotatable cutting tools.
Further, it would be highly desirable to provide such an improved rotatable cutting tool that has a hard cutting member wherein the hard cutting member maintains its integrity longer than hard cutting members in heretofore known rotatable cutting tools. This will result in an increase in useful life of the rotatable cutting tool as compared to heretofore known rotatable cutting tools.
In addition, it would be highly desirable to provide such an improved rotatable cutting tool that presents a braze joint that maintains its integrity longer than braze joints in heretofore known rotatable cutting tools. This will result in an increase in useful life of the rotatable cutting tool as compared to heretofore known rotatable cutting tools.
Furthermore, it would be highly desirable to provide such an improved rotatable cutting tool that presents a cutting tool body that experiences less “steel wash” as compared to heretofore known rotatable cutting tools. By providing a cutting tool body that experiences less “steel wash”, there will be an increase in the useful life of the rotatable cutting tool as compared to heretofore known rotatable cutting tools.